Multiphase polymer blends are of major economic importance in the polymer industry. Blending different polymers enables the production of new polymeric materials having an attractive balance of physical properties. For example, to enhance the impact strength of a brittle polymer such as polystyrene, small amounts of a rubbery polymer such as polybutadiene may be added to create a polymer blend which is tougher and more ductile than unblended polystyrene.
The development of useful polymer blends is difficult because of the inherent immiscibility of most polymers, which results in coarsely phase separated polymer mixtures in which the interfaces between components are compositionally sharp and mechanically weak. To overcome the problems created by inherently immiscible polymer blends, most commercial polymer blends consist of two polymers combined with small amounts of a third, compatibilizing polymer, such as a block or graft copolymer. In the polystyrene/polybutadiene example, a block or graft copolymer having polystyrene monomers and polybutadiene monomers may be used.
While the use of compatiblilizing polymers is effective in creating more stable blends of polymers, which would otherwise be immiscible, compatiblilizing polymers must be tailor made for the specific polymers used in a particular blend.